Mission 01BlinkMission 00Start hereMission 01Find the ExoplanetMission 02The Seven WorldsMission 03Reading an AtmosphereMission 04How Far Is That Star?Mission 05Weigh the Black HoleMission 06How Old Is the Universe?Mission 07The Planet Found on Paper
Mission 04
How Far Is That Star?
No spacecraft has ever left the solar system far enough to help. Every distance in astronomy rests on one measurement you can make from here: a nearby star shifts against the far background as Earth swings round its orbit, and the size of that shift is the distance.
01
Watch it shift
Look in June, then in December. Earth has moved two astronomical units and the near star has moved against the far ones.
02
Measure the angle
Half the total shift is the parallax. It is measured in arcseconds, and even the nearest star is under one.
03
Divide
One divided by the parallax in arcseconds is the distance in parsecs. That is the whole calculation.
Choose a star
Bright and near is easy. The faint distant ones are where the argument still is.